If the print strings in your game include only symbols from the ASCII (or Basic Latin)
character set -- values in the range 32..126 or $20..$7E --
then you probably don't need to read this.
The information here is all about how to address the Extended Latin characters:
mostly European accented letters with a few miscellaneous signs throw in for good measure.
If you wish to display such characters, you have four options.
Some carry disadvantages, which may affect which one you choose:

Insert them literally -- for example cause célèbre -- using whatever means your text editor provides for extending the keyboard repertoire.Disadvantage: Your source file isn't portable between IBM PCs and Apple Macs.
The word célèbre created on a PC might appear as cÈlËbre if that file was copied to a Mac,
because the two physical machines use different character encoding.

Use the Inform compiler's ability to embed internal character codes -- for example cause c@@170l@@182bre -- by typing @@ followed by a decimal number.Disadvantage: Your source file isn't portable between Z-machine and Glulx.
The word c@@170l@@182bre compiles to célèbre on the Z-machine, but to cªl¶bre when the target is Glulx,
because the two virtual machines use different character encoding.
(But remember: character codes in the range @@32 to @@126 are the same
in Glulx and the Z-machine. Thus, @@64 is "@", @@92 is "\",
@@94 is "^" and @@126 is "~" in both environments.)

Use the compiler's ability to embed escape sequences -- for example cause c@'el@`ebre -- by typing @ followed by a character pair.

Use the compiler's ability to embed UniCode values -- for example cause c@{E9}l@{E8}bre -- by typing @{..} around a hexadecimal number.

So, from this wealth of possibilities, we can deduce a couple of guidelines:

If you're not bothered about PC/Mac cross-platform compatibility --
because you work on a single platform and you've no intention of sharing your source code with anybody else --
use Option 1 because it's easiest to read.

If you're publishing source code, you really have to make it cross-platform,
so that means choosing one of the other options.
I recommend Option 3, since an escape sequence like @'e is easier to recognise as é
then either of the number-based options,
and it also makes your code portable between Z-machine and Glulx.

Also, you might take a look at Wouter ten Brink's cross-VM mapchar.zip
from the Archive.